Motor control.



R. H. MOLAIN.

MOTOR CONTROL.

APPLICATION FILED SEPT. 17, 1910.

1,039,568. Patented p -24,1912.

I YZTNE SES IYYENTUR 5' L RUBERT HMGLJZN w H25 ATTURNEY tion, instead ofgradually varying the readapted to bridge the UNITED STATES PATENTOFFICE.

ROBERT H. MCLAIN, 0F SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

MOTOR CONTROL.

Specification of Letters Patent.

, Patented Sept. 24, 1912.

Application filed September 17, 1910. Serial No. 582,502.

To all whom it may concern:

Be it known that I, Ronnnr H. MGLAIN, a citizen of the United States,

New York, have invented certain new and useful Improvements in MotorControl, of which the following is a specification.

This invention relates to the control of electric motors and has for itsobject the provision of means whereby the speed of an electric motor maybe automatically varied within predetermined limits by the opening andclosing of a control switch.

varying the field strength of the motor.

mon to increase the speed-of the motor, after it has been brought torunning speed, by 1nserting a resistance in series with the field of,

the motor, the speed being again decreased by the strengthening of thefield. This is commonly done by gradually cutting out or inserting theresistance either manually or.

automatically. In carrying out my invensistance of the field circuit, Ioperate upon the field resistance a whole by providing; means wherebythe resistance is alternately inserted or eliminated at a rapid rateuntil the motor finally reaches a speed corresponding to the ultimatefield strength desired. In

the practical embodiment of my invention I may employ an overload relayfor'short cir cuiting the resistance, the connections belng such thatthe contact member of the relay, will operate rapidly to open and closethe at a high speed corresponding to the field short circuit of theresistance.

gliagram showing my invention employed or as'employed for cit-herincreasing or decreasmg the speed of the motor.

Referring first to Fig. 1, A representsithearmature and F the shuntfield of. an electric,

motor. A resistance R is connected in series with the field F. A switch10 is connected in shunt with the resist-anceso as to short circuit theresistance. An overload relay 11, contacts 12 at a preresiding atSchenectady, county of Schenectady, State of decreasing the speed of themotor; and Fig. 3 1s a diagram showing the invention determined flow ofcurrent through the armature, is arranged in shunt to the switch 10 andresistance R. The mode of operation of this embodiment of the inventionis as follows: Assuming the motor to be running at normal speed and itis desired to increase the speed of the motor, the switch 10, which hasheretofore been closed, is opened. There being no excessive current inthe armature circuit, the contacts 12 of the relay 11 are not bridged.When the switch 10 is openedthe current in the field of the motor isreduced, thereby reducing the field magnetization and the motor startsto. speed up. At the same time there is an excessive current in thearmature circuit which causesthe overload relay 1]. to operate, therebyshort circuiting the resistance B. This momentarily increases thecurrent in the field circuit and likewise decreases the current inthearmature'circuit, causing the contact of the relay 11 to again drop'soas to open the short circuit on the resistance. The contact of the relay11 continues to vibrate, opening and closing a short circuit on theresistance, the speed all the time increasing until the motor finallv'reaches a speed correspondingto the strength of the field with theresistance R in series with it.

In Fig. 2 I have shown the invention employed for decreasing the speedof the motor.

In this case the switch 10 is in series with the contacts 12- of therelay 11 so that the switch 10 must be closed and the contacts 12bridged in order to short circuitthe resistance R in series with thefield F of the motor. Assuming the motor to be running strength with theresistance R in series with the field winding, the switch 10 will be,

open. If, now, it is desiredto reduce this speed, the switch 10 isclosed. This,-of course, short circuits the resistance B and suddenlystrengthens the field of the'motor.

This will cause the motor to operate as a generator and generate anexcessive current' through the armature A and the winding of the relay11 The short circuit on the resistance R will conse'quently be openedat.

the contacts 12 and the current in the field. circuit will be once morereduced. The contacts 12 will again be bridged and the current in thearmature circuit will be reduced causing the relay to drop. In this waythe relay will Vibrate backand fort-h, opening T insertion of theresistance R in circuit withthe field winding. While this vibrationislays.

and closing a short circuit on the resistance RE, the speed of the motorallthe time de-'. creasing until it finally reaches a speed whichcorresponds with the elimination of the resistance R from the fieldcircuit.

In Fig. 3 T have shown what is virtually a combinationbf Figs. 1 and2.In this case, by opening the switch 10 the motor will be graduallybrought up to a speed correspond-.

ing to the insertion of the resistance R", in

the field circuit F and 13 having their windings in series'with eachother and with the armature A. The

14* when the current is excessive.

series coil a shunt coil 15 be produced as is described in connectionwith Fig. 1. The relay 13 will vibrate to increase the speed of themotor until finally;

it corresponds to the speed produced by the taking place the relay 11does not operate since the shunt winding counteracts the efiect of theseries winding and holds the relay closed. If now the switch is closedthe same result will be produced as described; in connection with Fig.2. The current in the series coil of the relay 11 will now be reversedand acting in unison with the shunt coil, the direction of currentthrough which will open the relay and the vibration will continue untilthe speed of does not change,

the motor is reduced to that corresponding to the full field strength.While this vibration of the relay 11 is going on, the relay- 13 maylikewise operate but if it does, itwill have no efiect, since thecontacts are? From this it will be seen that the motor can be increased:or decreased in speed without having an ex shunted by the switch 10cessive armature current, by simply opening or closing the switch 10.

While I including various forms embodying concrete operating mechanismand connections, it is obvious that I do not limit my invention to theparticular applications herein described nor to the particular means forwhile when theswitch' is closed the speed of the motor will be re--duced to that corresponding to the elimination of the resistance R fromthe field ci'rcuit. In this case I providetwo relays l1.

have described my invention as;

nosaeoa carrying them out, except in so far as it is 'limitedby thescope of the claims annexed hereto.

Whatl claim as new and desire to secure by Letters Patent of the UnitedStates is 1. The combination with an electric motor, of means forvarying the speed thereof comprising a resistance for the field circuitof the motor and an overload relay responsive to variations in currentdue to the effect of said resistance which continuously opens andcloses'a short circuit on saidresistance until the motor reaches a speedcorrespondingto the predetermined field strength.

2. The combination with an electric motor, of means for varying thespeed thereof comprising a resistance for the field circuit ofxthemotor, and a normally short circuiting said resistance when closed, saidrelay being responsive to variations in current. due to the eifect ofsaid resistance so as to vibrate until the motor reaches a speedcorresponding to the field strength established by said resistance.

3. The combination with an electric motor, of means for varying thespeed thereof comprising a resistance or the field circuit of the motor,a switch for controlling said resistance, and a relay for automaticallyopening and closing aishort circuit on said resistance to bring themotor to a speed corresponding to the strength of the field as established by said switch.

4. The combination withan electric motor, of means for varying the speedthereof comprising a resistance for the field circuit of the motor, andmeans controlled by variations in the motor current due to the effect ofsaidv resistance for continuously opening and closing a short circuit onsaid resistance until the motor reaches a speed corresponding strength.

5. Th combination with an electric motor, of means for varyin comprisinga resistance %or the field circuit of the motor, a switch in shunt tosaid resistance, and a pair of relays, one of which operates toautomatically open-and close a short circuit on said resistance toincrease the speed of the motor when said switch is open, while theother operates to open'and close a short circuiton said resistance todecrease the speed of the motor when said switch is closed.

In witness whereof, I have hereunto set my hand the 16th day ofSeptember, 1910.

- ROBERT E. MoLAlN.

l Vitnessesz HELEN Onronn,

THOMAS W. NOONAN.

to the predetermined field open relay for the speed thereof

